They are not mentioned very often but they could make you some serious money.

There are a bunch of differences between a closed-end fund and an open-end -- or regular -- mutual fund.

They are bought and sold differently and a closed-end fund's portfolio could be a little riskier.

But that extra risk could mean extra upside -- higher dividends -- bigger returns. Of course it could also mean bigger downside and lower returns.

Want to Buy $1 Worth of Stock for 90 Cents or Less? You can with certain so-called "closed-end" mutual funds - an often overlooked investment class. Click here to register for a free online video in which TheStreet's retirement expert Robert Powell and an all-star panel tell you all you need to know. The webinar is sponsored by Nuveen.